The present invention relates to a process for polymerizing vinyl aromatic monomers, such as styrene, to produce polymers having a high degree of syndiotacticity, and more particularly to a process for preparing polymers of vinyl aromatic monomers having a high degree of syndiotacticity using an alkylaluminoxane-free catalyst. Such polymers may be usefully employed in the preparation of solid objects and articles such as a moldings, films, sheets and foamed objects by molding, casting or the like process.
In U.S. Pat. No. 4,680,353 there is disclosed a process for the preparation of polymers of vinyl aromatic monomers having a stereoregular structure of high syndiotacticity by the use of certain coordination catalysts. Particularly disclosed were the reaction products of a titanium compound and an organoaluminum compound, especially polymethylaluminoxane. The process disclosed in this patent, however, requires the use of large amounts of the polymethylaluminoxane which is very expensive and difficult to make due to its very complex structure. Also, this process requires an expensive polymer purification system to remove remaining catalyst components due to the use of large amounts of the polymethylaluminoxane.
In U.S. Ser. No. 8,800, filed Jan. 30, 1987 (published in equivalent form as EP 277,004) there are disclosed certain bis(cyclopentadienyl) metal compounds formed by reacting a bis(cyclopentadienyl) metal complex with salts of Bronsted acids containing a non-coordinating compatible anion. The reference discloses the fact that such complexes are usefully employed as catalysts in the polymerization of olefins. For the teachings contained therein, the aforementioned U.S. Ser. No. 8,800 and EP 277,004 are herein incorporated in their entirety by reference thereto.